1. Field of the Invention
This invention relates to controls for brake systems for multiple vehicle systems (i.e. tractor-trailer vehicles). In particular, this invention relates to controls for tractor-trailer brake systems which, depending upon the level of operator demand for braking, will distribute the braking effort between the individually controllable vehicle brake sites, such as between sub-vehicle brake systems, to achieve inter-vehicle balanced braking or proportional braking or a compromise thereof.
2. Description of the Prior Art
Brake systems, and the controls therefor, for vehicles, including heavy duty vehicles such as trucks, are, of course, well known in the prior art.
Brake systems for passenger cars are, in general, somewhat easier to design than brake systems for heavy duty vehicles such as tractor-trailer trucks as the loading of passenger vehicles will not vary to the extent loading will vary on a tractor only, a tractor with an empty or lightly loaded trailer or a tractor with a heavily loaded trailer.
Brake systems of the anti-lock type, for all types of vehicles, are well known in the prior art. Briefly, these systems operate to obtain a maximized vehicle stability (i.e. maximized transverse coefficient of friction of braked wheels) by maintaining the longitudinal slip of the braked wheels within predetermined limits. This usually requires modulating the braking forces on an individual wheel and/or individual axle basis to maintain at least some wheel rotation.
Examples of prior art anti-lock systems may be seen by reference to U.S. Pat. Nos. 3,767,270; 3,768,872; 3,854,556; 3,893,696; 3,929,383; 3,929,382; 3,966,267; 4,392,202 and 4,591,213, the disclosures of all of which are hereby incorporated by reference.
Brake systems which control braking to achieve a driver demand, sense driver demand in a "brake-by-wire" manner, sense coefficient of friction and modify brake forces accordingly, sense load on a wheel and modify braking effort accordingly, sense wheel slip and/or use electronic signals to achieve more rapid trailer brake response are also disclosed in the prior art as may be seen by reference to U.S. Pat. Nos. 4,140,352; 4,327,414; 4,494,199; 4,512,615; 4,545,240; 4,591,213; 4,606,586; 4,616,881; and 4,648,663, the disclosures of all which are hereby incorporated by reference.
While the prior art brake systems which modify braking effort in response to sensed parameters to achieve various goals, such as vehicle stability or the like, do, in general, provide enhanced vehicle braking, they are subject to further improvement as both inter-vehicle balanced and inter-vehicle proportional braking, depending upon operator demand, is not provided.